Dania Ahmed, 4, receives a polio vaccine at a health center in Baghdad on April 10. / Khalid Mohammed, AP

by Kim Painter, Special for USA TODAY

by Kim Painter, Special for USA TODAY

The spread of polio across international borders has become a global public health emergency, the World Health Organization said Monday.

The agency called for three countries, Pakistan, Cameroon, and Syria, to take measures to stop the international spread of the virus. WHO said it's especially important that residents and longtime visitors to those countries be vaccinated for polio before traveling and carry proof of vaccination.

The alert comes amid recent reports that polio has spread from Pakistan to Afghanistan, from Cameroon to Equatorial Guinea and from Syria to Iraq.

"If unchecked, this situation could result in failure to eradicate globally one of the world's most serious vaccine preventable diseases," WHO said in a statement.

Ten countries have polio within their borders and all should step up efforts to contain and control outbreaks, WHO says. The affected countries include Ethiopia, Somalia, Nigeria and Israel â?? though the virus has only been found in sewage and stool samples in Israel, according to a previous WHO report.

WHO reported 413 cases of polio worldwide in 2013. There have been 74 cases so far in 2014 and 59 of those occurred in Pakistan, the agency's Bruce Aylward said in a phone conference with reporters. No other country has had more than four cases this year, he said. But January through April is low season for the virus.

The polio virus spreads person to person. It infects the nervous system and can cause paralysis. The disease once was once thought nearly eradicated. The recent reemergence has been linked to stymied vaccination campaigns in conflict zones such as Pakistan and Syria.

"The reemergence and spread of polio out of Pakistan, Cameroon, and the Syrian Arab Republic is troubling and poses a serious threat to our ability to eradicate polio," says CDC Director Tom Frieden. "Conflicts in many areas where polio is circulating are hampering efforts to vaccinate, but success remains within reach."